Concrete construction element and process for making the same



y 25, 1965 w. J. SILBERKUHL ETAL 3,184,392

CONCRETE CONSTRUCTION ELEMENT AND PROCESS FOR MAKING THE SAME Original Filed Oct. 15, 1959 3 Sheets-Sheet 1 W/LHELM J SILBERKUHL ERNST HAEUSSLER INVENTORS.

h m Q Q Q 3 Sheets-Sheet 2 m k a r Q Q W Q mm m l W/LHELM J- SILBERKUHL ERNST HAEUSSLER INVENTORS.

May 25, 1965 w. J. SILBERKUHL ETAL CONCRETE CONSTRUCTION ELEMENT AND PROCESS FOR MAKING THE SAME Original Filed Oct. 15. 1959 May 25, 1965 w. J- SILBERKUHL ETAL 3,

CONCRETE CQNSTRUCTIQN ELEMENT AND PROCESS FO MAKI NG THE SAME Original Filed Oct. 15, 1959 3 Sheets-Sheet 3 W/L HELM J. SIL BE RK UHL ERNST HAEUSSLER INVENTORS.

AGENT United States Patent 2 Claims. (e1. 50-52) Our present invention relates to a construction element of prestressed concrete, adapted to be used, for example, in roof construction. The application is a division of our copending application Ser. No. 846,611, filed October 15, 1959.

In our co-pending application Ser. No. 796,818, filed March 3, 1959, jointly with Uwe and Kastl and now abandoned but replaced by application Ser. No. 168,700, filed January 25, 1962, as a continuation-in-part thereof, and also in application Ser. No. 715,750, filed February .17, 1958, by Wilhelm J. Silberkuhl, it has been shown that it is possible to produce concrete bodies, particularly for vault-type roofs, in which a concrete layer having a generally rectangular horizontal outline is supported on two opposite edges (normally the minor sides of the rectangle) and is substantially saddle-shaped so as to have a negative Gaussian curvature. It has been found that a concrete layer or shell so formed may be conveniently prestressed with the aid of internal tie rods extending at or near a straight-line generatrix of the saddle-shaped body which, in a typical case, will approximate a one-sheet hyperboloid or a hyperbolical paraboloid. Since a one-sheet hyperboloid is generated by revolution of a hyperbolic curve about its imaginary axis, and since this invention is concerned with shells of shallow cross-sectional curvature extending over only a small arc of a circle (generally less than a quadrant) which approximately coincides with a small segment of a parabola centered on its vertex, the expressions one-sheet hyperboloid and hyperbolical paraboloid as used herein are considered equivalent; they refer to a body characterized by the fact that any point of its surface is the intersection of two straight-line generatrices. The pair of straight-line generatrices intersecting at the geometrical center of a shell constituted by such body, passing substantially diagonally across its generally horizontal outline, form a suitable location for the imbedded tie rods. A body so prestressed, particularly if provided with supplemental reinforcements to distribute the effect of the prestressing means more or less uniformly over its peripheral zones, can be conveniently constructed without edge beams or similar external appendages.

It is an object of our present invention to provide a construction element of this general character, preferably but not necessarily incorporating the improvements disclosed in the commonly owned applications referred to above, which is of improved load-bearing capacity and can be more easily joined with other, similar members to form an unbroken structure.

Another object of this invention is to provide a novel construction element for roofs and the like which offers great resistance to flexural, shear and other stresses while being of relatively light weight and easily fabricated.

A more particular object of the invention is to provide an elongated, hollow, prestressed concrete member or beam which can be used not only as a roof support but also as a duct for heating or cooling fluids.

In accordance with this invention we provide a prestressed, substantially trough-shaped concrete shell of generally rectangular horizontal outline, preferably one 3,184,892 Patented May 25, 1965 having curvatures of opposite sign in mutually perpendicular planes, whose concave side is spanned by a cover plate statically consolidated with the shell along the major sides of the rectangle. The cover plate may be generally flat in transverse direction while partaking of the overall curvature of the shell in longitudinal direction. In accordance with another feature of the invention, however, it is possible to assemble the cover plate from a series of relatively short, flat elements adjoining one another in longitudinal direction with slight relative inclination to provide the necessary overall curvature. With a shell 10 to 20 meters in length, for example, each cover element can be a flat precast slab of about 1 meter in width, its length corresponding to the transverse dimension of the shell.

Advantageously, the shell is positioned with its concavity facing upwardly and the precast cover plate is joined with it while the concrete of the shell is still soft, a satisfactory bond being realizable in this manner if the precast elements are provided with projecting stirrups or similar anchor means and if their settling into the falsework-supported mass is accompanied by a vibrating of the assembly. The internal prestressing means for the shell may be tensioned at the same time against the falsework, as explained in the above-identified Silberkuhl application.

The covering elements, which could be either prestressed or provided with passive reinforcements, are preferably formed with lateral projections such as teeth which will increase the bond with the shell when sinking into the concrete of the latter. They may also be provided along their transverse edges with teeth or corrugations designed to afford abetter grip to a connecting layer of grout with which the gap between adjoining elements may be filled.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a perspective view of a construction element embodying the invention;

FIG. 2 is a cross-sectional view of a roof structure incorporating several supporting elements generally similar to that of FIG. 1;

FIG. 3 is a top plan view of part of the cover plate of one of the supporting elements of FIG. 2;

FIGS. 4 and 5 are cross-sectional views taken respectively on line IVIV and V-V of FIG. 3; and

FIG. 6 is a fragmentary perspective view of one of the supporting elements of FIG. 2 in an intermediate stage of manufacture.

In FIG. 1 we have shown an elongated, hollow concrete member 1 supported at its ends by means of piers 2, 3 (which are not part of the hollow concrete member 1). The member 1 consists of a prestressed, doubly curved shell 11 in the shape of a shallow segment of a one-sheet hyperboloid, facing upwardly with its concavity and presenting a generally rectangular horizontal outline. A cover plate 5, conforming to the curvature of shell 11 about its transverse axis, spans the concave side thereof and is firmly bonded to the upstanding edges 4 of the shell. A pair of tensioned cables 12 (see also FIG. 6) extend diagonally within the shell 11 along straight-line generatrices of the hyperboloid. Other reinforcements, not shown in FIG. 1, serve to distribute the stress of pretensioning members 12 over the marginal zones of the shell.

From FIG. 1 is will be noted that the shell 11 and the slab 5 are cambered upwardly in the longitudinal vertical plane of symmetry of member 1, in such manner that the horizontal plane in which the prestressing elements 12 are located, i.e. a plane passing substantially through the vertex of the shell, intersects the supported or outermost cross-sections of the shell (i.e. its cross- 0.3) sections in the regions of the piers 2 and 3) near the upper boundaries of these cross-sections in order to enable the cables 12 to pass substantially diagonally across the rectangular horizontal outline of the shell. It can be shown that a shell cambered strongly upwardly in this manner, having its vertex located at a level well above the centers of gravity of the supported outermost shell sections, subjects its curved longitudinal edges 4 to an inwardly directed transverse torque; this has been disclosed in our aforementioned US. patent applications Ser. Nos. 796,818 and 168,700. This torque, resulting from the dead weight of the unloaded shell and intensified by the live weight of the loaded structure, is resisted in thehollow beam illustrated in FIG. 1 by the compressive strength of the slab 5 whose curvature follows that of the shell edges 4 to which it is bonded. Since this slab thus prevents the inward curling of the shell edges, the shell 11 cannot be deformed from its hyperboloidal shape and its upward camber remains intact. As a result, the piers 2 and 3 need not absorb any axially directed stresses which would be exerted upon them if the shell were tending to sag under load.

Whereas in FIG. 1 the cover plate 5 has been shown as a unitary concrete layer, it is also possible and often desirable to assemble such plate from a plurality of shorter elements 5a, 5b, 50 etc. as illustrated-in FIGS. 36. These elements 50, 5b, 50 may be flat, precast slabs traversed by orthogonally extending, untensioned reinforcements 13 and 14. Stirrups 6 project from the side flanges of these plates which are also formed with teeth 7 along theundersides of these flanges. The slabs 5a etc. are also formed, along their transverse edges, with serrated recesses 8 which define'gaps 9 between adjacent plates; when the plates are positioned next to one another on their shell, the gaps 9 are filled with grout 16 to form a solid covering.

FIG. 2 illustrates how a plurality of hollow beams 101, 201 comprising shells 111, 211, slightly modified with respect toshell 11 of FIG. 1 by the provision of lateral ledges 17, can be bridged by cylindrically curved slabs 10 level with the slabs 5a etc. to form a barrelshaped roof with flat transverse section; the gaps between these slabs may be filled by grout 18. The slabs 10 may also be provided with windows as indicated at 10'. P16. 2 also illustrates the provision of unstressed reinforce: ments 19, 20 in the curved shell to serve as a means for distributing the prestressing forces.

FIG. 6 illustrates the manner in which the slabs 5a, 5b, 5c are assembled on the shell 111. As shown, these slabs are positioned with their flanges 15 above similar flanges 21 of shell 111 which at this instant is still supported by falsework not shown; the stirrups 6 and the teeth 7 of the cover slabs are then caused by controlled vibration to sink into the soft material of the shell flanges 21 so that, upon hardening, all the elements of the structure are joined together in a monolithic manner. When this is done, the gaps 9 are grouted in to complete the 1 of absorbing large bending momentsand will be particularly resistant to torsional stresses, owing to the stiifening action of the covering members 5, 5a, 5b, 5c. The invention is, however, not limited to the specific embodiments described and illustrated but may be realized in various modifications without departing from the spirit and scope of the appended claims.

What is claimed is:

1. A hollow beam comprising an upwardly concave horizontal concrete shell approximately shaped as a shallow segment of a one-sheet hyperboloid of substantially rectangular outline having parallel longitudinal edges, said shell being internally provided with elongated prestressing elements extending the full length of said shell substantially along the diagonals. of said rectangular outline along straight-line generatrices of said hyperboloid, and a concrete slab of substantially rectangular configuration conforming to said outline, said shell and said slab being cambered upwardly with identical curvature in the longitudinal plane of symmetry of said segment, said slab spanning the concave. side of said shell and being firmly bonded to it at said edgesto form an integral unit therewith.

2. A hollow beam comprising an upwardly concave horizontal concrete shell approximately shaped as a shallow segment of a one-sheet hyperboloid of substantially rectangular outline having. parallel longitudinal edges, said shell being internally provided-with elongated prestressing elements extending the full length of said shell substantially along the diagonals of said rectangular out line along straight-line 'generatrices of said hyperboloid, and a plurality of rectangular concrete cover plates spanning the concave side of said shell, said plates being firmly bonded to said shell at said edges to form an integral unit therewith and adjoining one'another in longitudinal direction of the shell and in mutually bonded'relationship to constitute a unitary slab'of substantially rectangular configuration conforming to said outline, said shell and said slab being cambered upwardly with identical curvature in the longitudinal plane of symmetry. of said segment.

References Cited by the :Examiner UNITED STATES PATENTS OTHER REFERENCES 7 Journal of the American Concrete Institute publication, January 1955, pp. 397-415. V

JACOB I. NACKENOFF, Primary Examiner. WILLIAM I. MUSHAKE, Examiner. 

1. A HOLLOW BEAM COMPRISING AN UPWARDLY CONCAVE HORIZONTAL CONCRETE SHELL APPROXIMATELY SHAPED AS A SHALLOW SEGMENT OF A ONE-SHEET HYPERBOLOID OF SUBSTANTIALLY RECTANGULAR OUTLINE HAVING PARALLEL LONGITUDINAL EDGES, SAID SHELL BEING INTERNALLY PROVIDED WITH ELONGATED PRESTRESSING ELEMENTS EXTENDING THE FULL LENGTH OF SAID SHELL SUBSTANTIALLY ALONG THE DIAGONALS OF SAID RECTANGULAR OUTLINE ALONG STRAIGHT-LINE GENERATRICES OF SAID HYPERBOLOID, AND A CONCRETE SLAB OF SUBSTANTIALLY RECTANGULAR CONFIGURATION CONFORMING TO SAID OUTLINE, SAID SHELL AND SAID SLAB BEING CAMBERED UPWARDLY WITH IDENTICAL CURVATURE IN THE LONGITUDINAL PLANE OF SYMMETRY OF SAID SEGMENT, SAID SLAB SPANNING THE CONCAVE SIDE OF SAID SHELL AND BEING FIRMLY BONDED TO IT AT SAID EDGE TO FORM AN INTEGRAL UNIT THEREWITH. 